Ingestion of plastics at sea: does debris size really matter?

Most of our knowledge on plastic ingestion by zooplankton comes from experiments exposing invertebrates to plastic particles smaller than their feeding apparatus. By examining millimetre-sized marine plastics using a scanning electron microscope, we putatively identified some surface textures as feeding marks produced by invertebrates grazing upon the plastic biofilm. We observed sub-parallel linear scrapes with 5-14 μm spacing, which is similar to typical distances between teeth of the mandibular gnathobases of copepods. We also observed peculiar rounded marks close to an unidentified marine worm. Small portions of the plastic particles were apparently removed, and perhaps ingested, during these putative grazing activities. Thus, we suggest that (1) plastic biofouling induces plastic ingestion, and (2) plastic pieces must not necessarily be smaller than the organism for a feeding interaction to occur. Experiments exposing invertebrates to millimeter-sized plastics may support these suggestions.